1. Field of the Invention
This invention relates generally to devices for removing component parts from a stack and using them in the assembly of an article of manufacture, and more particularly relates to a method and apparatus for removing component parts from the bottom of a stack of parts to permit supplying of the stack from the top.
2. Description of the Related Art
In the field of microsurgery, a surgical instrument having a cutting blade traverses a specific path through tissue. One feature of the surgical instrument is a single-use cartridge that is a holder for surgical staples. The cartridge is an elongated plastic body with a longitudinal channel that serves as a guide for a surgical blade. The cartridge has rows of small staples on opposite sides of the channel, and these rows are aligned parallel to the guide channel. Drivers are inserted in apertures (also called “pockets”) aligned with the rows in order to push the staples out of the cartridge and through the adjacent tissue. Before the blade has made its cut, each side of the incision is stapled together by displacing the drivers relative to the cartridge. This displacement forces the staples against an anvil on the opposing side of the surgical instrument as the cartridge and the anvil deflect the points of the staples into a clasping position.
There may be as many as fifty or more very small staples on each side of a two-inch incision. Each staple can be driven into the tissue to close the incision by the correspondingly small drivers. The task of inserting the drivers into the cartridge is labor-intensive due to the small size and number of the drivers and the apertures.
One prior art system for mounting the staple drivers into apertures in the cartridge includes a plastic holder, commonly referred to as a “tree” having aligned “branches” with drivers integrally formed on an end of each of the aligned branches. The conventional cartridge is placed in an apparatus and the tree with drivers is hand-manipulated to place the drivers adjacent the entrance to the pockets. This is normally accomplished by inserting the drivers in funnel-shaped passages that are aligned with the pockets. Each driver is subsequently driven into the associated pocket of the cartridge. The separation of the individual drivers from the branch of the tree on which it is mounted is accomplished by flexing the branches of the tree manually to break the tree away from the staple drivers. Then, a hand-manipulated tool is used to press each staple driver down into the cartridge to near the pocket opening on the opposite side of the cartridge.
The finger operation of pressing each driver into a pocket, the flexing of the branches and the subsequent pressing from the hand-operated prongs can misalign some of the drivers within the pockets. Furthermore, the sizes of the pockets and the drivers vary slightly due to the minute structure involved and the fact that both the cartridge and the staple drivers are formed of thermoplastic resin, which does not always result in a perfectly formed structure. This combination of factors can cause some “play” in the assembly, which can result in an alignment problem. In particular, inversion of the cartridge after assembly can result in some of the drivers being displaced from their pockets. If a staple driver is absent, no staple will be driven into the tissue at that point in the incision.
Another problem is the imprecision in the process of separating the staple drivers from the branches of the plastic “tree”, a process referred to as “degating.” The drivers are mounted to the tree prior to insertion in the cartridge, but must be removed from the tree before or during the insertion process. Because the separation of a driver from the tree is not precise, it leaves some material on one side of each driver. The remnants of material left on the drivers is not a predictable size, and often the remnants are larger than desired. While it is not practical to remove all of the holder material from the side of each driver in the separation process, it is important that the amount of material left on each driver be relatively consistent between drivers. This is because the material left on the side tends to cause friction when the staple driver is used in surgery. If the amount of material left is consistent, it allows a user of such a staple cartridge to accurately predict the amount of force needed to expel a staple in surgery. In addition, the smaller the volume of material left, the less friction will be generated, and the less the force required to use the staple cartridge.
It is known in the prior art to insert drivers mechanically into surgical stapling cartridges, as shown in U.S. Pat. No. 5,836,147 to Schnipke, U.S. Pat. No. 5,653,928 to Schnipke, U.S. Pat. No. 6,158,205 to Schnipke et al., and U.S. Pat. No. 7,207,168 to Doepker et al., all of which are incorporated herein by reference. Workers manually position the cartridges, as well as the holders that contain the drivers and hold them relative to the machine, in the machines disclosed in these patents, and then actuate the machine to insert the tiny drivers into the pockets in the cartridges. After a fraction of the total number of drivers is inserted by one machine, the cartridge is then manually transported to the next machine, which inserts another fraction of the drivers. In U.S. Pat. No. 6,729,119 to Schnipke et al., which is incorporated herein by reference, a robotic loader is described for use in filling the cartridges discussed herein with the use of fewer workers than the prior art.
The machines disclosed in the patents referenced above, although representing a significant improvement over the prior art, still require parts to be fed in batches to the machines. This requires periods of time in which the machine is not operating in order to supply components to the machines. Thus, there is a need for an apparatus that permits continuous feeding of component parts to the above machines, and to other machines that are unrelated to the above.